Azeotropic distillation of aliphatic hydrocarbons having the formulas cnh2n and cnh2n-2 from hydrocarbon mixtures comprising same



Oct. 8, 1946.

AZEOTROPIC DISTILLATION OF ALIPHATIC HYDROCARBONS HAVING THE FORMULAS Guan AND nml-.9.V

H. S. NUTTING ETAL Umweg/md 0,7 '605 FROM Q'IYDROCARBON MIXTURES COMPRISING SAME Flled July 29, 1939 ATTORNEYS Patented Oct. 8, 1946 nach UNITED STATES PATENT OFFICE Howard S. Nutting and Lee H. Horsley, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application July 29, 1939, Serial No. 287,218

22 Claims. l

This invention concerns an improved .method of separating unsaturated aliphatic hydrocarbons having the formulas Cul-ign and CnHzn-z, particularly diolenes and acetylenes containing from 3 to 6 carbon atoms in the molecule, from hydrocarbon mixtures comprising the same.

ln the industrial cracking of hydrocarbon materials such as petroleum fractions, coal tar distillate, etc., complex mixtures of gaseous or low boiling liquid hydrocarbons which comprise parafiins, olelnes, diolenes and acetylenes are produced in large quantities and the separation o1" such mixtures to recover the individual hydrocarbons in even technically pure form constitutes a serious problem. For instance, when an organic product such as kerosene or other petroleum fractions, cyclohexane or other cycloparaiiin, cyclohexene, ethylene, etc. is pyrolized gaseous or low boiling mixtures comprising butadiene-1.3 and one or more of the isomeric butylenes, e. g. butylene-l, butylene-Z, or isobutylene is fractionally obtained. Other hydrocarbons such as ethylene, propylene, ethane, propane, butanes, etc. may be and usually are present in the mixture. It is true that such mixture of saturated and unsaturated hydrocarbons may be separated by distillation into fractions consisting for the most part of hydrocarbons containing the same number of carbon atoms to the molecule, but each such fraction usually consists of a mixture of saturated and unsaturated hydrocarbons which can be separated from one another only with diioulty, or not at all, by further rectiiication. For instance, such distillation of the crude pyrolysis mixture may be carried out to obtain a fraction consisting ior the most part of a mixture of butane, butylene, butadiene, and ethyl-acetylene, and by very eiiicent rectification it is possible to obtain at least partial separation of the two compounds butane and ethyl-acetylene from the mixture. However, the butylene and butadiene distill together and cannot satisfactorily be separated from one another by ordinary rectification regardless of how carefully or efficiently the operation is carried out. A number oi' methods for separating certain unsaturated hydrocarbons such as butylene and butadiene from one another are known, but these involve operations other than distillation, e. g. extraction with a selective solvent, reaction of one or more of the hydrocarbons in the mixture with an added chemical reagent such as sulphuric acid or cuprous chloride, etc. By suitable combinations of such known methods it may be possible to separate all of the individual hydrocarbons from a crude pyrolysis mixture, but obviously such complete separation would be difficult and expensive due to the knumber of diiierent operations and the variety of equipment required.

An object of this invention is to provide a relatively simple and inexpensive method whereby a crude gaseous or low boiling hydrocarbon mixture comprising an olene and a diolene and/or an acetylene may be separated into its components by a single type oi operation, viz. distillation. The primary object is to provide an improved method of distilling any low boiling hydrocarbon mixture containing at least two different kinds of unsaturated hydrocarbons of very nearly the same boiling point, e. g. a mixture of two or more of the compounds butylene-l, butadiene-1.3 and ethyl-acetylene, to recover the individual unsaturated hydrocarbons in relatively pure form. Other objects will be apparent from the following description of the invention.

We have discovered that whereas an olene and a diolefine having the same number of carbon atoms in the molecule usually boil at very close to the same temperature and cannot satisfactorily be separated from one another by ordinary rectincation at atmospheric or increased pressure, such separation may readily be accomplished by carrying the distillation out in the presence of ammonia. The ammonia forms an azeotropic mixture with the olene and another-azeotropic mixture with the diolene. The azeotrope of each hydrocarbon with ammonia boils at a temperature below that of the ammonia or the corresponding hydrocarbon alone, but the aZeotropes have boiling points and heats of vaporization sufficiently divergent from one another to permit separation by distillation at atmospheric or superatmospherio pressure. The difference between the distilling temperatures of the two azeotropes becomes slightly greater as the pressure on the listilling system is increased. However, the latent heats of vaporization of the two azeotropes diverge considerably with increasing pressures. In all instances, the azeotrope of ammonia with an olene (or with a parain hydrocarbon) varies only slightly in composition as the pressure is increased, but the ammonia content of the aZeotrope of ammonia with a diolene increases markedly as the pressure on the distilling system is raised. By carrying such distillation with ammonia out at a pressure suicient to avoid necessity for refrigeration in order to liquefy the distilling vapors, e. g. at a pressure of pounds per square inch gage or more, separation of the azeotropes is rendered most practical.

We have discovered another fact which is of interest in this connection. The ease of separating an oleiine from a mixture thereof with a diolene having the Same number of carbon atoms, which is brought about by distilling such hydrocarbon mixture under pressure with ammonia, is apparently due not only to the divergence between the distilling temperatures of the azeotropic mixtures formed, but also to the divergence between the heats of vaporization of the two azeotropes. To illustrate this point, it may be mentioned that the azeotropio mixtures of ammonia with butylene and with butadiene which are formed at a pressure of 175 pounds per square inch gage, have, at said presurse, boiling points of approximately 30 and 33 C., respectively. Although two substances having so nearly the same boiling temperature are usually difcultly separable or non-separable from one another by distillation, these two azeotropes may be separatedl without difficulty. This apparently is because the lower boiling azeotrope requires far less heat for Vaporization than does the higher boiling azeotrope, so that within the distilling column a large amount of heat liows rapidly from the azeotrope of ammonia and butadiene (i. e. the higher boiling azeotrope), during its condensation, to the lower boiling azeotrope of ammonia and butylene, thereby maintaining the latter azeotrope largely in vaporized condition and giving rise to much sharper fractionation than would be expected in View of the proximity of the boiling points of the two azeotropes.

We have also found that certain unsaturated hydrocarbons which may be separated from one another by ordinary distillation in the absence of ammonia, may not be separated readily during distillation with ammonia. An example of this type is the mixture of butadiene and methylacetylene. These two compounds have different boiling points and are separable by fractional distillation. However, ammonia forms with butadiene and methyl-acetylene two azeotropes which are difficult to separate by distillation; hence, the

presence of ammonia interferes with the separal tion of these hydrocarbons. In general, we find that the presence of ammonia facilitates the separation of an oleiine from a dioleiine or an acetylene containing the same number of carbon atoms in its molecule, but that ammonia interferes with the separation by distillation of a diolefine from an acetylene having one less carbon atom than the dioleiine per molecule.

We have further found that any hydrocarbon mixture containing lower unsaturated aliphatic hydrocarbons which tend to distill together may, regardless of the number or identity of the hydrocarbons present, be rectified to recover each individual unsaturated hydrocarbon in a form substantially free of other unsaturated hydrocarbons, by carrying the rectiiication out in successive stages, ammonia being present in certain stages of the rectication, but absent in others. More particularly, we have found that the diolefines and the acetylenes having from 3 t0 6 carbon atoms in the molecule which are present in the hydrocarbon mixture may, by rectification as just described, be isolated as individual compounds of good purity, i. e. as individual compounds of greater than 80 per cent and usually greater than 95 per cent purity.

The accompanying drawing is a flow sheet showing one series of operations which may be employed in separating as relatively pure compounds the diolenes and acetylenes often found in cracked-oil gas. In the rectification scheme indicated by the flow sheet it will be noted that not only are the diolelines and acetylenes each separated in fairly pure form, but also each oleine of the crude gas mixture is recovered in a form substantially free of other unsaturated compounds.

In recovering from cracked-oil gas the olenes, dioleflnes and acetylenic hydrocarbons contained therein, as indicated in the drawing, we first liquefy the crude gas and then fractonally distill the liquefied material, preferably while maintaining it at superatmospheric pressure. Methods for carrying out this distillation, which is accomplished in the absence of ammonia, are wellknown, and this initial distillation step is not claimed per se, but only in combination with the other distillation operations that go to make up our complete process. By this initial distillation without ammonia there is obtained a low boiling fraction containing methane, ethane, and ethylene; a second fraction consisting largely of propane, propylene, propadiene and methyl-acetylene; a third fraction consisting largely of butano, butylene, butadiene and ethyl-acetylene; a fourth fraction of pentane, amylenes, pentadienes (largely isoprene) and pentynes; and a fifth fraction consisting for the most part of hexane, hexenes, hexadienes and hexynes. Higher boiling material may, for the purpose of the present invention, be discarded.

Any one of the fractions 2-5 thus obtained is then introduced along with liquid ammonia into a still and is fractionally distilled in the presence of the ammonia. This distillation may be carried out in continuous or batch-wise manner, but continuous distillation is preferred. During this distillation with ammonia there may be obtained as a distillate a mixture of ammonia, the paraffin hydrocarbon, and the olene, e. g. a mixture of ammonia, butane and butylene, designated in the drawing as sub-fraction tAf and as a residue fraction a mixture of ammonia, the diolene, and the acetylenic hydrocarbon, e. g, a mixture of ammonia, butadiene and ethyl-acetylene, designated as sub-fraction B.

Each fraction is treated to separate the amrnoniaJ from the hydrocarbons therein and the ammonia is returned to the distillation. This treatment of a fraction to remove the ammonia may be effected in any of several ways, the preferred procedure being dependent upon the particular hydrocarbons present. The parailin hydrocarbons containing 5 or more carbon atoms per molecule are practically insoluble in liquid ammonia; hence, when a fraction of distillate contains a large proportion of such hydrocarbons, mechanical separation of the ammonia from the hydrocarbons is usually possible. On the other hand, the unsaturated hydrocarbons containing 5 carbon atoms to the molecule are, at room temperature or above, soluble in ammonia, and those containing 6 carbon atoms are somewhat less soluble; so that when a fraction contains these hydrocarbons it may be necessary to cool to room temperature or below in order to effect satisfactory mechanical Separation of the ammonia from the hydrocarbons. The hydrocarbons containing 3 or 4 carbon atoms to the molecule are very soluble in liquid ammonia at room temperature and cooling to below 10 C., preferably below 0 C., is usually required in order to break the solutions of these hydrocarbons in ammonia and mechanically separate the latter. The small proportion of ammonia remaining with the hydrocarbons after such separation may be removed by washing with water or otherwise; however, removal of the residual ammonia is usually not necessary in order to carry out the successive steps of the process.

The mixture of diolenic and acetylenic hydrocarbons, e. g. butadiene and ethyl-acetylene, thus obtained is then distilled in the absence of ammonia, preferably at a pressure sufcient to permit condensation of the distillate Without need for refrigeration, to obtain the individual hydrocarbons in substantially pure form.

By such successive distillations (in the presence of ammonia and then in its absence) of any one of the fractions 2-5 of the hereinbefore mentioned initial distillation, the unsaturated hydrocarbons in suc-h fraction are recovered in a form substantially free of other unsaturated compounds. Thus from the initial fraction containing the hydrocarbons having 4 carbon atoms to the molecule, butylene may be recovered in admixture with butane, but in a form practically free of other unsaturated hydrocarbons, and butadiene and ethyl-acetylene may each be recovered in purified form, i. e. in a form of greater than 90 per cent purity. These same operations, when applied to the fraction of the initial distillation which contains propane, propylene, propadiene and methyl-acetylene, result in the recovery of propane and propylene as one nal fraction and in the recovery of propadiene and methyl-acetylene each as an at least technically pure compound. Similarly from the fraction of the initial distillation consisting of hydrocarbons having 5 carbon atoms to the molecule, a fraction of pentane and pentene is obtained and the pentadiene and pentyne in the starting material are separated from one another. Isoprene of greater than 80 percent purity (the impurities apparently being one or more isomers of isoprene) has been recovered in the process. The fraction of the initial distillation which consists for the most part of hydrocarbons containing 6 carbon atoms to the molecule may likewise, by such successive distillations with and without ammonia, be separated into a fraction consisting of hexane and hexene, and into other fractions consisting of hexadiene and hexyne, respectively.

It has hereinbefore been mentioned that in any of the steps involving distillation with ammonia, each fraction of distillate containing ammonia and one or more hydrocarbons is, when suiciently cooled, a mixture (rather than a solution) of ammonia and the hydrocarbons. The hydrocarbons containing less than 5 carbon atoms to the molecule are of lower density than liquid ammonia; hence, on cooling a solution of such hydrocarbons and ammonia sufficiently to cause separation of the ammonia, the latter forms a lower layer. The hydrocarbons having more than 5 carbon atoms to the molecule are of greater density than ammonia; hence on cooling suciently to break a solution of these hydrocarbons and ammonia, the ammonia separates as the upper layer. On the other hand, the hydrocarbons containing 5 carbon atoms to the molecule have practically the same density as that of liquid ammonia. Accordingly, when a solution of these hydrocarbons and ammonia is cooled sufliciently to break the solution, little, if any, of the ammonia separates as a distinct layer; instead a heterogeneous liquid mixture results. This mixture is readily broken by adding just a trace of Water or any other substance which is soluble in only one of the components of the mixture and which, when dissolved in that component,wil1 change its density suii'iciently to cause separation.

The general procedure described above may be modied without departure from the invention. For instance, instead of initially distilling a liquefied cracked-oil gas in the absence of ammonia to obtain individual hydrocarbon fractions, each of which consists for the most part of a mixture of hydrocarbons having the same number of carbon atoms per molecule, the initial distillation of the crude hydrocarbon mixture may, if desired, be carried out in the presence of ammonia. Such initial distillation in the presence of ammonia changes, of course, the composition of each of the individual fractions obtained. For instance, such distillation of liqueed cracked-oil gas with ammonia usually results in the amylenes and butadiene being recovered in one fraction and the pentadienes and pentynes being recovered in another fraction. However, the various fractions of distillate obtained by such initial distillation in the presence of ammonia may then each be redistilled in the absence of ammonia to further separate the hydrocarbons contained therein. For instance, the hydrocarbon fraction comprising amylenes and butadiene obtained in such initial distillation with ammonia may be redistilled in the absence of ammonia to separate the amylene and butadiene from one another.

Any of the distillations of a hydrocarbon fraction comprising an olene, a diolene and an acetylene in the presence of ammonia may be carried out in Ways other than those hereinbefore described. For instance, the mixture of butane, butylene, butadiene, and ethyl acetylene hereinbefore mentioned may be distilled in the presence of just sufficient ammonia to distill off the butane and butylene in azeotropic admixture with the ammonia. The distillation may then be continued in the absence of ammonia and the butadiene and ethyl acetylene thereby be separated from one another. As alternative procedure, distillation of the hydrocarbon fraction comprising an olene, a diolene and an acetylene may be carried to completion in the presence of ammonia to obtain a first fraction of ammonia and the olene and a second fraction of ammonia, the diolene and the acetylene. The second fraction may then be treated to remove the ammonia and be redistilled in the absence of ammonia to separate the diolelne and acetylene from one another.

Although cracked-oil gas, because oi its complexity, was chosen as the starting material in the foregoing general description, the invention is not restricted to the treatment of cracked-oil gas. Instead, it may be applied in separating any dioleine or acetylene containing between 3 and 6 carbon atoms, inclusive, from any aliphatic hydrocarbon mixture regardless of the source of the latter. For instance, the relatively simple mixture of butane, butylene, butadiene and ethylacetylene produced by the pyrolysis of butano may be treated in accordance with the invention to separate the unsaturated hydrocarbons from one another.

The following examples illustrate certain ways in which the principle of the invention `nas been applied, but are not to be construed as limiting the invention.

EXAMPLE' 1 The purpose of this example is to summarize in schematic form our findings as to the various 7 fractions -of distillate that are obtainable by distilling a mixture -of paraiin hydrocarbons, olenes, diolenes and acetylenes containing from 3 to 6 carbon atoms to the molecule under various conditions. In the distillation schemes indcated in the following table, the starting material is in each instance a hydrocarbon mixture .containing parain hydrocarbons from propane to hexane, olefnes from propylene to hexene, diolenes from propadiene to hexadienes, and acetylenic hydrocarbons from methyl-acetylene .to hexynes. Each distillation is carried out under pressure in the presence or in .the absence of ammonia as indicated. The table gives the various fractions of distillate that are obtainable, depending upon Whether or not ammonia is present during .the distillation.

The following Table II shows the fractions of distillate that are obtainable by starting Ithe distillation of a liqueed hydrocarbon mixture (similar to that employed in Example 1) in the presence of suicient ammonia Ito form azeotropes with the propane and propylene and, after this initial charge of ammonia is removed by distillation, periodically adding more ammonia as indicated. The distilling scheme indicated in the table has resulted in the separation of diolenes and acetylenes. Butadiene of greater than 99 per cent purity has been separated from such mixtures in this manner.

TABLE II Alternate distillation without and with NH3 Starting in the presence of ammonia dstill off:

Fractions No Identity {Propane-l-NHa Propylene-I-NHa 2 Methyl-acetylene Add NH3 to .the still residue and Acontinue the distillation in the presence of NH3 to obtain:

Fractions No. Identity Butanes-l-NHa 3 {l utylenes+NH3 4 Butadiene 5 Ethyl-acetylene Add more ammonia .to the residue and continue distillation to obtain:

Fractions 5 Identity {Pentanes-NHH Amylenes-i-Nla Pentadienes Pentyncs Fractions N o. Identity 9 {Hexanes-I-NH; Hexenes-i-NH;

l0 Hexadlenes ll Hexynes EXAMPLE 3 415 pounds of liquid ammonia and 1025 pounds of a, liqueed cracked-oil gas fraction, containing 502 pounds of butylene (mostly butylene-1), 502 pounds of butadiene-1.3, and 2l pounds of acetylenes (mostly ethyl-acetylene), were introduced in steady flow separately but simultaneously into a continuous still which was operated at a pressure of between 150 and 200 pounds per square inch gage and at a still-head temperature of about C. to distill oif the azeotrope of ammonia and butylene. The distillate Was cooled during operation t0 obtain partial separation of the ammonia from .the hydrocarbons therein, and the ammonia so-separated Was returned continuously to the distillation. Butadiene was withdrawn continuously from the lower end of the distilling column. During (the distillation there was collected 715 pounds of distillate (containing about 454 pounds of butylene, 238 pounds of ammonia, and 22 pounds of butadiene) and there was withdrawn from the bottom of the still 465 pounds of material containing 446 pounds of butadiene, 9 pounds of acetylenic hydrocarbon (largely ethylacetylene), 5 pounds of butylene and 5 pounds of ammonia. The distillate was washed with Water .to remove the ammonia, thus leaving butylene of approximately 95 per cent purity, i. e. containing only 5 per cent of butadiene. The higher boiling material withdrawn from the bottom of 'the distilling column was likewise treated to remove ammonia, leaving butadiene of 97 per cent purity, i. e. containing only 1.9 per cent of acetylenic hydrocarbon and 1.1 per cent of butylene.

At the close of the distillation, the distilling column was cooled to condense and drain out its inventory of refluxing material. This reflux inventory, which amounted to 146 pounds and consisted of approximately 103 pounds of ammonia, 27

pounds of butadiene, 15 pounds of butylene, and

1 pound of acetylenic hydrocarbon, is retained in the still column during continuous operation.

EXAMPLE 4 Cracked-oil gas was liquefied and distilled at superatmospheric pressure to separate a fraction consisting for the most part of hydrocarbons having 5 carbon atoms to the molecule. Approximately 1750 grams of this hydrocarbon fraction and 1100 grams of liquid ammonia were charged into a still and the mixture was fractionally dis' tilled at superatmospheric pressure. During the distillation, 2500 grams of additional ammonia was added in small portions and compressed nitrogen was fed into the distilling system to build up pressure and thereby facilitate condensation of the distillate. The nitrogen was fed into the condenser for the distillate. The pressure during the distillation varied from 1GO pounds to 440 pounds per square inch gage and the distilling temperature, i. e. the temperature at the head of the distilling column, varied from 29 to 59 C., this temperature varying with the pressure. The distillation at superatmospheric pressure was continued until a fraction rich in pentadienes was obtained. The remaining volatile material was then distilled at atmospheric pressure without attempt at fractionation. The fractions obtained are described in the following table which gives the per cent by volume of ammonia in each fraction of distillate and also the identity of the hydrocarbons present and the molal per cent of each kind of hydrocarbon based on the total hydrocarbons in the fraction. The procedure in analyzing fraction 1, i. e. the lowest boiling fraction, was to wash it with water to remove the ammonia, redistill it in the absence of ammonia to remove and identify the butadiene therein, and then to treat the mixture of higher boiling hydrocarbons chemically in known manner, first to remove the 1.3-diolefines, e. g. 1.3- pentadienes, then to remove the monoalkyl acetylenes, i. e. pentynes. The hydrocarbons remaining after these treatments Were scrubbed successively with aqueous sulphuric acid solutions of 63 per cent and 87 per cent by Weight concentrations, respectively, to remove by absorption the other unsaturated hydrocarbons present. The hydrocarbons absorbed in the acid consist of olenes, 1.2- or 1.4-diolenes and dialkyl acetylenes. In the table, they are termed other unsaturated hydrocarbons. The substances not absorbed in any of these treatments consisted of parafns and air. They are referred to in the table as inerts The other fractions of distillate Were similarly Washed with Water to remove the ammonia and an aliquot portion of the remaining hydrocarbons Was analyzed as just described, except that the step of distilling oir butadiene (which not not present to appreciable extent) Was, of course, omitted. Itmay be mentioned that fraction 9 in the table is the material that was distilled at atmospheric pressure without fractionaton.

The pentadiene-LS in the above fractions 3, 4, and 5 was found to be isoprene.

Although the invention, as hereinbefore pointed out, is particularly applicable in separating from one another olenes, diolenes and acetylenes containing from 3 to 6 carbon atoms in the molecule, it may also be employed in separating higher unsaturated hydrocarbons, e. g. oleilnes, diolenes, and acetylenes containing 7 or 8 carbon atoms per molecule, from their mixtures. At any given distilling pressure, the hydrocarbon content of the azeotropes of ammonia With hydrocarbons of an aliphatic series, e. g. the oleiine series or the dioleiine series, becomes lower as hydrocarbons of increasing boiling point are employed. Accordingly, a smaller proportion of ammonia is required in separating unsaturated hydrocarbons having from 3 to 6 carbon atoms from one another in accordance with the invention than is required in eiecting a similar separation of the higher unsaturated hydrocarbons.

This application is a continuation in part of our co-pending application Serial No. 199,600, filed April 2, 1938.

Although the following claims indicate that the separation of unsaturated hydrocarbons by distillation in the presence of ammonia in accordance With the invention involves the formation of one or more azeotropes of ammonia With the hydrocarbons, it will be understood that the fractions obtained during such distillation 'do not necessarily have the compositions of such azeotropes.

Other modes of applying the principle of the invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

We therefore particularly point out and distinctly claim as our invention:

1. In a method of separating an unsaturated TABLE III Hydrocarbons, inolel per cent of total NH3 content Fraction Volume No. cc. pegy Bum: Penn? Other unsatdienel.3 dienes-LS Pentmes'l gggbg Inerts 1 2, 000 79. 3 27. 5 0 2. 7 60. 5 9. 3 2 l, 700 69. 4 0 0. 5 0. 9 88. 8 9. 8 3 400 80 0 2. 5 1. 3 73. 7 22. 5 4 300 80 0 2. 6 7. 9 73. 6 15. 9 5 300 80 0 4. 5 0 81. 8 13. 9 6 200 9() 0 8 3 v 78. 0 11. 0 7 300 90 0 15 2 70. 0 13. 0 8 300 90 0 24 54 22. 0 9 350 0 0 54 25 2l. 0

Fraction 9 was then fractionally distilled at atmospheric pressure in the absence of ammonia to obtain the following fractions, each of which was analyzed as in the initial distillation:

aliphatic hydrocarbon containing more than 2 and less than 7 carbon atoms in the molecule and having the empirical formula CnI-Izn-z from a mixture of hydrocarbons comprising the same and a more saturated hydrocarbon having the same number of carbon atoms in the molecule, the steps which consist in forming a mixture oi ammonia with the hydrocarbons to be separated from one another and fractionally distilling the resultant mixture at a pressure not substantially lower than atmospheric pressure, whereby a relatively low boiling azeotrope of ammonia and said more saturated hydrocarbon is formed, the iractional distillation in the presence ol ammonia being continued until a substantial proportion ol the more saturated hydrocarbon has been separated from the hydrocarbon of formula CnHzn-a 2. In a method of separating a dioleine which contains more than 2 and less than 7 carbon atoms in the molecule from a hydrocarbon mixture comprising the same and a more saturated olene having the same number of carbon atoms in the molecule, the steps which consist in adding ammonia to the hydrocarbon mixture and fractionally distilling at superatmospheric pressure, whereby a relatively low boiling azeotrope of ammonia and said more saturated olene is formed, the fractional distillation in the presence of ammonia being continued until a substantial proportion of the more saturated olene has been separated from the dioleine.

3. In a method wherein a hydrocarbon mixture comprising an acetylene, a diolene, and a more saturated hydrocarbon, each having more than 2 and less than 7 carbon atoms per molecule and all having the same number of carbon atoms in the molecule, is fractionally distilled to obtain a primary fraction and the primary fraction is redistilled, the steps of carrying one oi said distillations out in the presence of added ammonia at a pressure not substantially lower than atmospheric pressure, whereby a relatively low boiling azeotrope of ammonia and the more saturated hydrocarbon is formed and continuing this distillation in the presence of ammonia until a substantial proportion of the more saturated hydrocarbon is separated in a form relatively free of the acetylene and diolene, and carrying the other distillation out at a pressure not substantially lower than atmospheric pressure in the absence of ammonia, whereby said hydrocarbons containing more than 2 and less than 7 carbon atoms and having the same number of carbon atoms in the molecule are separated from one another.

4. In a method of separating butadiene from a hydrocarbon mixture containing the same and a more saturated olene having the same number of carbon atoms in the molecule, the step of fractionally distilling the hydrocarbon mixture at superatmospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the more saturated olene is formed and continuing the distillation in the presence of ammonia until a substantial proportion of the more saturated olene is separated from the butadiene.

5. In a method wherein a liquefied hydrocarbon mixture comprising an acetylene, a diolene, and an olene, each having 4 carbon atoms in the molecule, is fractionally distilled to obtain a primary fraction and the latter is redistilled, the steps which consist in carrying one of said distillations out at a pressure not substantially lower than atmospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the olene is formed, and ,continuing this distillation in the presence of ammonia until a substantial proportion of the olenne is separated in a form relatively free of the acetylene and diolene, and carrying the other distillation out at a pressure not substantially lower than atmospheric pressure in the absence of ammonia, whereby the acetylene, dioleiine, and olene are at least partially separated from one another.

6. In a method of separating the components of a mixture of hydrocarbons comprising an acetylene, a diolene, and a more saturated hydrocarbon, each having more than 2 and less than '7 carbon atoms per molecule and all having the same number of carbon atoms in the molecule, the steps which consist in fractionally distilling the liqueiied mixture at superatrnospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the more saturated hydrocarbon is formed, continuing this distillation in the presence of ammonia until a substantial proportion of the more saturated hydrocarbon is separated in a form re1- atively free of the acetylene and diolene and thereafter continuing the distillation in the substantial absence of ammonia to separate the diolene from the acetylene hydrocarbon.

7. In a method of separating the components of a mixture of hydrocarbons comprising an acetylene, a diolene, and a more saturated hydrocarbon, each having 4 carbon atoms in the molecule, the steps of fractionally distilling the liquefied mixture at superatmospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the more saturated hydrocarbon is formed, continuing this distillation in the presence of ammonia until a substantial proportion of the more saturated hydrocarbon is separated in a form relatively free of the acetylene and diolene, and thereafter continuing the distillation in the substantial absence of ammonia to separate the diolene from the acetylene hydrocarbon.

8. In a method of separating a diolelne which contains more than 2 and less than 7 carbon atoms per molecule from a hydrocarbon mixture containing the same and a more saturated olene having the same number of carbon atoms in the molecule, the steps of fractionally distilling the liquefied mixture at superatmospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the more saturated oleiine is formed and continuing this distillation in the presence of ammonia until a substantial proportion of the more saturated olefne is separated in a form relatively free of the diolene, while separating ammonia fromv the distillate and returning the separated ammonia to the distillation.

9. The method which comprises separating from cracked oil gas a liquefied mixture comprising hydrocarbons having more than 2 and less than 7 carbon atoms in the molecule, fractionally distilling the liquefied mixture to obtain a fraction consisting substantially of hydrocarbons having the same number of carbon atoms in the molecule and comprising an acetylene, a diolene, and an olene, fractionally distilling such mixture at superatmospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the olefine is formed and continuing this distillation in the presence of ammonia until a substantial proportion of the olene is separated in a form relatively free of the acetylene and diolene, and continuing the distillation in the substantial absence of 13 ammonia to separate the diolefine from the acetylene.

.10. In a method of separating butadiene-1.3 from a mixture thereof with a butylene, the steps of adding ammonia to the liquefied hydrocarbon mixture and fractionally distilling at a pressure not substantially lower than atmospheric pressure, whereby a relatively low boiling azeotrope of ammonia and the butylene is formed and continuing the distillation until a s-ubstantial proportion of the butylene is separated from the butadiene.

11. In a method of separating butadiene-1.3 from a mixture thereof with butylene-1, the steps of adding ammonia to the liquefied hydrocarbon mixture and fractionally distilling at a pressure not substantially lower than atmospheric pressure, whereby a relatively low boiling azeotrope of ammonia and the butylene-1 is formed and continuing the distillation in the presence of ammonia until a substantial proportion of the butyl- Y ene-1 has been distilled together with ammonia, leaving a residue consisting substantially of butadiene-1.3.

12. In a method of separating an acetylene which contains more than 2 and less than '7 carbon atoms in the molecule from a hydrocarbon mixture thereof with an olefme containing the same number of carbon atoms in the molecule, the step of distilling the hydrocarbon mixture at super-atmospheric pressure in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the olene is formed and continuing the distillation in the presence of ammonia until a substantial proportion of the oleiine is separated from the acetylene.

13. In a method for separating from one another the unsaturated components of a mixture of hydrocarbons comprising an acetylene having 4 carbon atoms in the molecule, butadiene-1.3, and a butylene, the steps of fractionally distilling the liqueiied mixture at a pressure between about 100 and about 440 pounds per square inch in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and the butylene is formed, continuing this distillation in the presence of ammonia until a substantial proportion of the butylene is separated in a form relatively iree of the acetylene and the butadiene- 1.3, and thereafter continuing the distillation in the substantial absence of ammonia to separate the butadiene-1.3 from the acetylene,

14. In a method of sep-arating an aliphatic hydrocarbon having the empirical formula CuHzn-z and containing more than 2 and less than 7 carbon atoms in the molecule from a mixture of hydrocarbons comprising the same and a more saturated hydrocarbon having the same number of carbon atoms in the molecule, the steps which consist in forming a mixture of ammonia with the hydrocarbons to be separated from one another and fractionally distilling the resultant mixture at a pressure between about 160 and about 440 pounds per square inch while introducing an inert gas into the distilling system to create at least part of the pres'- sure on said system, whereby a relatively low boiling azeotrope of ammonia and the more saturated hydrocarbon is formed, and continuing the distillation in the presence of ammonia until a substantial proportion of the more saturated hydrocarbon is separated from the unsaturated hydrocarbon of empirical formula CnHzn-z.

15. In a method for separating from one another the unsaturated components of a mixture of hydrocarbons comprising an acetylene having 4 carbon atoms in the molecule, butadiene- 1.3, and a butylene, the steps of fractionally distilling the liquefied mixture at a pressure between about and about 440 pounds per square inch in the presence of added ammonia and an inert gas, whereby a relatively low boiling azeotrope of ammoniaand the butylene is formed, continuing this distillation in the presence of ammonia until a substantial proportion of the butylene is separated in a form relatively free of the acetylene hydrocarbon and the butadiene-L3, and thereafter continuing the distillation in the substantial absence of ammonia to separate the butadiene-1.3 from the acetylene.

16. In a method of separating butadiene-1.3 lfrom a hydrocarbon mixture comprising the same and a butylene, the step of fractionally distilling the liquefied mixture at a pressure between about 100 and about 440 pounds per square inch in the presence of added ammonia and an inert gas, whereby a relatively low boiling azeotrope of ammonia and the butylene is formed, and continuing this distillation in the presence of ammonia until the ammonia and butylene have been distilled from the butadiene, whereby the latter is obtained in a form relatively free of the butylene and ammonia.

17. In a method of separating butadiene-1.3 from a mixture thereof with isobutylene, the steps of fractionally distilling the liquefied hydrocarbon mixture in the presence of added ammonia, whereby a relatively low boiling azeotrope of ammonia and isobutylene is formed, and continuing the distillation in the presence of ammonia until a substantial proportion of the isobutylene has been separated from the butadiene.

18. In a method of separating butadiene-1.3 from a mixture thereof with isobutylene, the steps of forming from the hydrocarbon mixture and ammonia a liquefied mixture of ammonia and the hydrocarbons and distilling at a pressure of at least 100 pounds per square inch a mixture of ammonia and isobutylene which comprises an azeotrope of said compounds to leave the butadiene in relatively pure form as residue from the distillation.

19. In a method for separating from one another the unsaturated components of a mixture of hydrocarbons comprising butadiene-1.3 and isobutylene, the steps of fractionally distilling the liquefied mixture at a pressure between about 100 and about 440 pounds per square inch in the presence of added ammonia and an inert gas, whereby a relatively low boiling azeotrope of ammonia and isobutylene is formed, and continuing the distillation in the presence of ammonia until a substantial proportion of the isobutylene is separated from the butadiene-1.3.

20. A process for concentrating diolens contained in a, mixture thereof with mono-olens possessing vapor pressures of the same magnitude, which comprises distilling said mixture in the presence of liquid ammonia to produce a vapor fraction containing the major portion of said mono-olei'lns, and a residue containing the major portion of said diolens.

21. In a method of separating butadiene from a mixture thereof with a butylene, the steps of fractionally distilling the liquefied mixture at superatmospherie pressure in the presence of added ammonia, whereby an azeotrope of amthe liqueed hydrocarbon mixture in the presence of added ammonia, whereby an azeotrope or ammonia and the amylene is formed and distilled, and continuing the distillation in the presence of ammonia, until a substantial portion of the amylene has been separated from the isoprene.

HOWARD S. NUI'IING. .LEE H. HORSLEY. 

